Effect of Gd addition on phase formation, microstructure, and mechanical performance of a CoCrFeNi multi-principal element alloy

Abstract

Here, two multi-principal element alloys (MEPAs): CoCrFeNi and CoCrFeNiGd0.05 are fabricated by high-energy ball milling and spark plasma sintering. The effect of Gd on microstructure and mechanical properties of the CoCrFeNi MPEA is investigated. The addition of Gd to the CoCrFeNi base alloy leads to precipitation of a GdNi5-type phase with hexagonal structure (HS) and minor amounts of a Gd-rich oxide phase from the FCC matrix. Compared to the CoCrFeNi base alloy, the grain size of CoCrFeNiGd0.05 is smaller, and the tensile yield strength of CoCrFeNiGd0.05 significantly increases from 546 MPa to 859 MPa, along with minor sacrifices in plasticity where the elongation only slightly decreases from 20.8% to 19.4%. The enhanced strength of Gd-containing MPEA is mainly attributed to grain boundary strengthening from the ultrafine-grained microstructure and the precipitation strengthening contributed by the HS phase. Transmission electron microscopy (TEM) results demonstrate that the GdNi5-type intermetallic phase is coherent with the FCC matrix and shows the following orientation relationship: {111¯}FCC//{2¯119¯}HS. The high plasticity of the composite-structured CoCrFeNiGd0.05 alloy is attributed to the homogenous distribution of the ultrafine HS phase and the coherent HS-FCC interface facilitating dislocation slipping.

Keywords

• Multi-principal element alloy
• Rare-earth element
• Microstructure
• Mechanical properties
• Intermetallics